A conventional cassette insertion device of the general type identified above is shown in FIG. 5. As shown in FIG. 5, a digital audio tape cassette 1 has a lid 2 for covering its tape-running plane, a slider 3 for locking the lid 2 in the closed position, and a pawl 4 insertable in a hole 3a formed through the slider 3 so as to lock the slider. A holder 5 holds and carries the tape cassette 1 so as to set the same in a tape running mechanism when the tape cassette 1 is inserted into the holder 5. The holder 5 has a first projection 5a which is formed on its upper inner surface and is brought into contact with the upper surface of the tape cassette 1. Formed on the lower inner surface of the holder 5 is a second projection 5b for urging the pawl 4 upwardly to release the locking of the slider 3. Also formed on the lower inner surface of the holder 5 is a claw 5c for engagement with the front end face of the slider 3 so as to slide the slider upon insertion or pushing-in of the tape cassette 1.
When the tape cassette 1 is inserted in the holder 5, the upper surface of the tape cassette 1 is urged downwardly by the first projection 5a, and the pawl 4 is urged upwardly by the second projection 5b. Therefore, the locking of the slider 3 by the pawl 4 engaged in the hole 3a is released, thus enabling the sliding of the slider 3.
The tape cassette 1 is then further pushed into the holder 5, so that the front end of the slider 3 is brought into engagement with the claw 5c. Therefore, when the tape cassette 1 is still further pushed into the holder, the slider 3 is caused to slide to a position near a lower projection 6 formed on the lower surface of the tape cassette 1, so that the locking of the lid 2 is released, as shown in FIG. 5.
In such a cassette insertion device, when the tape cassette 1 is accidentally inserted in the wrong direction, with the lid 2 directed inwardly, as shown in FIG. 6, the second projection 5b gets trapped in a recess lying between the lower projection 6 on the tape cassette and the slider 3. Since the upper surface of the tape cassette 1 is urged downwardly by the first projection 5a, it is difficult for the lower projection 6 to slide over the second projection 5b in its withdrawing direction.